Light guides, also indicated as wave guides, are known per se. They are used, inter alia for spreading the light across a relatively large light emission surface and are used, for example, in backlighting units of non-emissive displays such as liquid crystal display devices, also denoted LCD panels. Such backlighting units are used, for example, in TV sets and monitors or displays of, for example, (portable) computers or (portable) telephones. Light guides may also be used for spreading light across an emission surface of a general lighting system used in general illumination applications which may be used for illuminating parts of, for example, homes, offices, public buildings, shops and even roads. Alternatively such light guides may, for example, be used for illuminating advertising boards.
The known light guides typically confine a part of the light inside the light guide for mixing the light before the mixed light is extracted from the light guide and emitted by the light guide. The extraction of the light from the light guide may be done using known extraction means, such as scratches or indentations in the light guide. The extraction of light may also be done via diffusing the light in the light guide, for example, using diffusion centers or scattering material distributed in the light guide.
Such backlighting system for illuminating an image display device is, for example, known from the patent application WO 02/35245. The backlight system from the cited patent application comprises a light-emitting panel having a front wall and, opposite thereto, a rear wall and opposite first and second light transmitting edge surfaces associated with a plurality of first and second light sources. Light originating from the light sources is diffused in the panel. Parts of the surface areas of the rear wall are provided with extraction means for extracting light from the panel. Light emitted by the light sources is partially confined in the light panel via total internal reflection and is extracted from the light panel via extraction means. The extraction means comprise wedge-shaped indentations in the panel for extracting light from the light panel. A disadvantage of the known illumination system is that the production of the extraction means is relatively complex.